What distance is a half marathon?

A half marathon is 21.0975 kilometres, exactly half the marathon distance, or about 13.11 miles. The tool uses that precise figure so the per-km and per-mile pace and the checkpoint splits are accurate.

What is the target pace band?

It is a window of plus or minus 1.5% around your goal pace per km. Holding goal pace to the second every kilometre is unrealistic, so the band gives you a practical range; staying inside it on every kilometre keeps you on track for your goal.

Why are splits shown every 5K?

Five-kilometre checkpoints are easy to read on a watch and match the markers on most courses. The table lists the cumulative time you should see at 5, 10, 15 and 20 km plus the finish on even pace.

How should I pace the back half?

Keep the first 10 km comfortably inside the band and resist surging. The back half of a half marathon is where pacing errors surface, so arriving at 15 km on target with energy in reserve is the goal.

Is even pace the best strategy?

For most runners, even pace or a very slight negative split produces the best half marathon result. Going out hard feels easy early but the cost compounds after 15 km, which is why the tool centres on an even-pace plan.

Half Marathon Pace Calculator

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The half marathon is long enough that small early pacing errors compound badly in the final five kilometres. A clear goal pace, a realistic band to hold it in, and 5K checkpoints give you the structure to run an even, well-judged race.

How it works

The half marathon distance is fixed at 21.0975 km, so pace and checkpoints follow directly:

pace per km   = totalSeconds / 21.0975
pace per mile = totalSeconds / 13.1094
target band   = pace per km × 0.985  to  pace per km × 1.015
checkpoints   = pace per km × {5, 10, 15, 20, 21.0975}

The band acknowledges that you cannot hold goal pace to the exact second every kilometre; staying within roughly 1.5% is the practical target.

Example and tips

For a 1:45:00 goal, the pace is about 4:59 per km (around 8:01 per mile) with the 10 km checkpoint near 49:48 on even pace. Keep the first 10 km inside the band and hold something back for the final 6 km, where most positive splits in the half marathon are won or lost.